This is my pretty standard Leona build. She is a very fun support to play requiring some very well timed skill shots to be any good with and some patience. I think in higher ELO's she's not as viable but in lower ELO she seems to be a pretty solid support role choice as people don't seem to know how to dodge as well. enjoy.

PROS
-amazing CC and tankyness
-scary burst early game when coordinated with ad
-very fun to play
-good initiator

CONS
-you cannot heal your ad carry so they need to be careful and probably buy boots and health pots first.
-can only start out with 1 ward so use it wisely
-damage buy herself? lol
-any team that's not mildly affected by downs will just ignore you. (most low ELO don't)

zomg a tank/support getting gold runes and quints? yes, your a tank and a support, leona sucks at farming due to her passive only proccing from ally attacks, get over it. she's not a solo top, or jungler or any weird nonsense. Play like a support, get support quints and seals, that means avarice runes.

as mentioned in the runes section. your a support, therefore spec like one. get the gold regeneration talents, the increased ward effectiveness, etc. standard 0/9/21 build, nothing special there.

I've tried heal, and it just doesn't seem to work out with CV and now a days it's become popular for the ad carry to bring a heal, so yah, don't bother. flash is a good choice being both offensive and defensive in nature. I shouldn't have to explain the CV. Knowing the location of the enemy is crucial. It may not be the glorious ignite or w/e summoner skill you want, but if you have any handle on jungle routes it can save multiple lanes if your clever and your not even near them. How cool is that?

this should look fairly similiar for all standard supports with a few exceptions. No, I don't like getting aegis of the legion. it seems kinda lack luster to me honestly and zekes herald is much shinier for the added c/d reduction (which should cap you at 40% pretty early) and the added attack speed and lifesteal and added health. This is a very useful item to have since its not like your a soraka that can just run around mindlessly healing and infusing yourself. YOU SHOULD ALWAYS BE NEXT TO YOUR CARRY, ESPECIALLY AFTER YOU GET THIS ITEM. I don't care if they're going to the bathroom, you hold their hand and follow them in. No matter what.

In early levels she can seem fairly weak. However, upon hitting 3 and especially six leona starts to get scary. With an even halfway coordinated jungler gank you can almost always ensure the ad carry kill in bot lane assuming you can land all your shots (W,E,Q,R). I find that Leona's work very well with bursty ad champs such as vayne and tristana. Vayne really needs time to work up those silver bolt procs and with the nerf to her movement speed catching enemies can be frustrating. Well fear no more fellow Vayne players, Leona's can hold down and enemy champ for... (how many seconds do all those stuns add up too?) well enough time to ensure a kill.

upon entering mid game phase you are the initiator and tower diver if the circumstances are right, and you at least have your giants belt. if you see a 2v1 situtation in your favor at their tower, take it. Be a bully. You're Leona and should be able to CC the enemy champ under their own tower, tank it, and let a buddy grab the kill.